1. Field of the Invention
The present invention generally relates to a battery charging system, and in particular to a system for charging a rechargeable battery such as a lithium-ion battery and a rechargeable battery pack for use in the system.
2. Description of the Related Art
Recently, a rechargeable battery or a secondary battery has been widely used as a power supply for portable or hand-held electronic equipment in consideration of running costs. Such a rechargeable battery has predetermined charging conditions including charging current and time. Especially in the case of a rechargeable lithium-ion battery, the details about charging conditions have been defined.
In general, a constant-voltage and constant-current charging method is used to charge a rechargeable lithium-ion battery. More specifically, the rechargeable lithium-ion battery is charged with a constant current until the battery voltage has risen to a predetermined charge control voltage and thereafter with a constant voltage. Such a charging method has been disclosed in U.S. Pat. No. 5,237,259, for example.
There has been commercially available rechargeable lithium-ion batteries having different prescribed voltages. Therefore, it is necessary for a single battery charger to provide a plurality of charge control voltages each corresponding to the prescribed voltage of a rechargeable lithium-ion battery. To cope with this, the battery charger may be provided with a plurality of constant-voltage circuits which are selectively used depending on the type of a rechargeable lithium-ion battery pack. The battery charger is further provided with a battery type identifying means. And the rechargeable lithium-ion battery pack is provided with a battery type indicating means. When the battery pack is electrically connected to the battery charger, the battery type identifying means of the battery charger identifies the type of the lithium-ion battery by checking the battery type indicating means of the battery pack. According to the battery type, the battery charger provides the corresponding constant voltage to the battery pack after the battery voltage has risen to the predetermined charge control voltage.
However, the rechargeable lithium-ion battery pack needs the battery type indicating means and the charger needs the battery type identifying means. Therefore, it is difficult to miniaturizing the size and weight of the batter charging system as well as the battery pack.